Conventionally, there has been none of such a transmitting and receiving system installed in a dangerous area or in an automobile, but only warning signs for informing of the road situations are installed on the road. Therefore, when a driver runs a road for the first time or during a night, if he or she is encountered with a sharp curve or a steep slope suddenly, it is difficult for him or her to become ready to the situation, thereby being led to an accident often. Particularly, even if the driver is accustomed to the road, if the situation of the road is changed by road constructions and the like, the driver can fail to adapt to the new situation (that is, the driver can not exert a defensive vigil, but can drive in a careless manner), with the result that a large scale accident can occur sometimes.